Method of preparing electrolyte



Jan. 17, 1956 1 R, YOUNG ET Al.

METHOD 0F PREPARING ELECTRQLYTE Filed Jan. 2l, 1955 u@ ss Nmb.

xNvEN-roRs Thomas l?. ,Voz/n Kobe/' L. Somefgme BY y ,M @M

ATToRNEYs IV E -mit United States Patent METHoD or PREPARINGELEc'rRoLYTE Thomas R. Young, Riverside, Conn., and Robert L.

Somerville, Neshanic, N. J., assignors, by mesne assignments, toHorizons Titanium Corporation, Princeton, N. J., a corporation of NewJersey Application January 21, `1953, Serial No. 332,327 4 Claims. (Cl.2011-64) This invention relates to the electrolytic production `ofmetallic titanium and metallic zirconium and, more particularly, to a.cyclic method wherein `spent electrolyte from the titanium or zirconiumproduction stage may be completely recovered and re-used in theelectrolytic operation.

The production of metallic titanium and metallic zirconimn byelectrolytic deposition from `a fused `salt bath containing an alkalimetal-titanium or zirconium double liuoride (an alkali metaltluotitanate or iluozirconate) has `been developed to the stage wherethe metal so produced is of high purity. From a commercial standpoint,however, the cost of producing metal by this procedure is a seriousdrawback due largely to the cost of raw materials including the liuorine`component of the double .fluoride. We have now discovered that the costof raw materials for such a process of electrolytically producingmetallic titanium and metallic zirconium can be markedly reduced byappropriate choice of the diluent salt bath and by appropriateconversion of the by-products :of the electrolysis. Thus we have foundthat the completely cyclic handling of all by-products of theelectrolysis may be .achieved without the buildup of any one .or more ofthe elements of the electrolytic bath. r

The success of `our recyclic operation in the .electrolytic productionof metallic vtitanium or metallic zirconium from a fused salt bath isdependent upon the `use as the immediate source of the titanium orzirconium of -a :compound of such metal the anion `of which isrestricted to `one or more of the elements chlorine, oxygen and carbon,by the use as `another component of the salt bath of one or more alkalimetal chlorides, and advantageously `by the use `of hydrogen, as theonly other extraneous raw material, for conversion of by-productchlorine from the electrolytic cell into hydrogen chloride for use inthe transformation of the titanferous or Izirconiferous `source materialinto the corresponding alkali `metal double uoride. Thus, our inventioncomprises an improvement in -the proA duction of metallic titanium ormetallic zirconium wherein a double iiuoride of titanium or zirconiumand an alkali metal is electrolyzed `in a fused salt bath comprisingthis double fluoride `dissolved or otherwise contained in `an `alkalimetal chloride, the-:products of the electrolysis comprising depositedmetallic titanium or zirconium, evolved chlorine gas and an alkali`metal iluode-cont`aining spent electrolyte. Our improvement in such aprocess comprises reacting the `spent `electrolyte from the aforesaidelectrolysis `with. hydrochloric acid and a titaniferous orzirconiferous source material the anion of which is cbmposed of one -ormore of the `elements chlorine, oxygen and carbon with the resultingformation of an alkali metal-titanium or `zirconium double iuoride andan alkali `metal chloride which areithereafter used as `the doubleuoride and alkali metal components of the aforementioned `fused saltbath. .In `the presently preferred embodiment of `our invention, the.hydrochloric -acid .is rde rived by the reaction of .chlorine evolvedvfrom .the electrolytic cell with extraneous hydrogen.

, 2,731,405 Patented Jan. 17, 1956 The titaniferous sources .useful inpracticing our invention include oxidic compounds such as titaniumdioxide, titanium carbonate and titanium oxychloride (TiOCla) andtitanium carbide. Each `oit' these source materials should be suppliedin as pure form as readily available in order to preclude the build upof extraneous impurities in the process. When titanium dioxide is usedas the starting material, we have found it advantageous to use anatasetitanium dioxide pigment, but other forms of the dioxide may be usedwith advantage. The oxychloride of titanium as well as the carbonate andcarbide are 'available and can be used as the source of titanium withoutintroducing into the cyclic process any component which will be built upto the detriment of the operation of the process.

The zirconiferous materials useful in practicing our invention includeoxidic zirconiferous materials such as zirconium oxides, zirconiumcarbide and zirconium oxychloride. Thus, inasmuch as the raw materialsas Well `as the chemistry of our process are substantially the same forzirconium as for titanium, we shall contine our subsequent descriptionof the invention to the production of metallic titanium with 'theunderstanding, of course, that what is said in this regard applies withequal force to the .corresponding production of `metallic zirconium.

The only other raw material required in signiiicant amounts for thepractice of our invention is hydrogen, `and this hydrogen may besupplied either as such or in the form of a mixture of propane and steamwhich, when burned in lthe presence of chlorine gas, will yield hydrogento react with the chlorine to form hydrogen chloride.

The process of our invention will be readily understood by referencetothe accompanying flow sheet. As shown therein, an alkalimetal-titanium double fluoride, such as potassium titanium fluoride(also known as potassium tiuotitanate, KzTiFs), `and at least one alkalimetal chloride -such as sodium chloride are charged `to an electrolyticcell 1 as the essential components of the electrolytic bath. The cellJis heated to maintain these salts in fused condition `in the cell.Electrolysis of the resulting bath, which may contain, for example, 2:to 30% `by weight of the `double `iiuoride, results in the depositionat the cell cathode of metallic titanium which may be `removed in .anyappropriate manner. Chlorine gas is evolved at the anode and iswithdrawn from the cell and Aburned with hydrogen in a combustion-chamber 2. The resulting hydrogen chlorideis advantageously absorbed inwater in an absorption tower 43, and the resulting aqueous hydrochloricacid is .delivered `to a reactor 4 wherein the alkali metal-titanium.double fluoride is produced. Spent elecxtrolyte is withdrawn from thecell either intermittently or continuously, and is delivered to thereactor 4. This spent electrolyte, which `contains an alkali metaliiuoride as its essential component, may be either cooled and -thencharged directly to the reactor 41or it may be broken up into .aslurrywith extraneous water or other suitable wash iiquid from another stageof the process and be delivered in this form to ithereactor4.

The .other `primary component delivered to the reactor 4 comprises thetitaniferous source material such as titanium .dioxide or titanium`oxychloride. If titanium dioxide is used, it may be charged to thereactor in the form ,of d-ry titania pigment. .Of course, when thetitaniferous nmaterial -is charged Lin the form of oxychloride, lesseramounts of hydrochloric acid will be required and any l,excess acidproduced :from the cell chlorine maybe dis posed of or u sed .in anyother desirable way. Small amounts ,of an `alkali metal chloride such aspotassium chloride and arsource of Vtluorine such as hydrotluoric acid,may also be .added to the rreactor 4 in order to `make up Vtoranymechanical loss `offthealkali metal-, chlorineand ilumine-components ofthe fused salt bath and thus insure 'i .a the presence in the reactor ofsubstantially stoichiometric quantities of all essential reagents forthe formation of an alkali metal-titanium double uoride.

inasmuch as the electrolysis of the fused salt bath is preferablycarried out under an inert atmosphere, advantageously of a monatomic gassuch as argon, the argon will be discharged from .the cell along withythe chlorine. How ever, the argon will pass-through the combustionchamber 2 and the absorption tower 3 and can thus be returned to l thecell 1 preferably with intervening purification to remove any extraneousgas such as nitrogen from leakage or carbon dioxide from the burning ofpropane, or to remove a gaseous impurity introduced into the systemalong with the argon.

The reaction between the added titaniferous source ma terial, thegenerated hydrochloric acid and the recirculated spent electrolyte,together with added make-up reagents, takes place in the reactor 4 uponheating this mixture to a temperature close to the boiling point ofwater at atmos -pheric pressure, i. e. to up to about 100 C., by meansof steam coils orV the like. The resulting alkali metal `titanium doublefluoride solution, such as a potassium-V titanium fluoride solution; iswithdrawn from the reactor 4 and is concentrated to crystallize out ofthe solution both -the double iiuoride vand a portion of the containedalkali metal chloride. We have found that this result can be ob tainedparticularly satisfactorily in a triple effect evapo rator, butregardless of the method of separating the double fluoride and thealkali metal chloride these separated salts are passed through driers 5and 6 and thence back to the electrolytic cell 1. yIt will be seen,accordingly, that theV only extraneous source materials for this continuous production of titanium metal comprises the ti taniferous sourcematerial, such as titanium dioxide, and hydrogen for the generation ofhydrogen chloride from the chlorine effluent from the cell.

As pointed out hereinbefore, we have found that a triple effectevaporator may be used with particular ad vantage in the recovery of thesolid alkali metal-titanium double fluoride and alkali metal chloridefrom the solu tion thereof withdrawn from the reactor 4. In theoperation of the triple effect evaporator in accordance with ourinvention, the alkali metal-titanium double fluoride and alkali metalchloride solution (such, for example, as an aqueous solution ofpotassium titanium uoride and sodium chloride) is delivered to the thirdeffect of the evaporator. The solution is concentrated in the thirdyeffect by the combination of a reduction in pressure, such as operationunder a vacuum of say 27 inches of mercury, and by the heat supplied bysteam which has previously been used as the heating medium for the firsttwo effects. The liquor in the third` effect is thus concentrated at atemperature of about 50 C. with the result that potassium titaniumfluoride crystals form in the liquor. The resulting slurry of thedoublefluoride is discharged from the third effect to a separator 7, and theseparated double uoride is delivered to the drier 5. A portion of themother liquor removed from the double uoride in the separatorV 7 maybe'returned to the reactor 4 and the remainder of the liquor isydelivered to the second effect of the evaporator. Inasmuch as theysecond effect operates at a higher temperature, generally about 90 C.,the further evaporation of water from the liquor introduced into thesecond effect from the separator 7 results in crystallization of sodiumchloride. The resulting slurry is discharged from the second'effect to aseparator 8 from which the separated sodium chloride is delivered to thedrier 6. A

portion of the liquor separated from the sodium chloride i in theseparator 8 is advantageously returned to the third effect and theremainder of this liquor is delivered to the first effect of theevaporator. Inasmuch as the heating steam for the evaporator passesthrough the first effect before the second and third effects, thetemperature of the liquor in the first effect is raised to a stillhigher temperature, aboutV 130 C. Although a considerable amount of 4water is evaporated from the liquor in the first effect, with theresulting crystallization of some sodium chloride, the resulting slurryis delivered to the second effect Where further evaporation, though at alower prevailing operating temperature, effects more completecrystallization of sodium chloride which is then recovered in theseparator 8. On the other hand, the potassium titanium fluoridecontained in the aqueous phase in both of these relatively hightemperature effects will remain in solution and will not crystallizefrom the solution to any significant extent until it is delivered to thethird effect which, as noted hereinbefore, advantageously operates at arelatively low temperature of about V C.

The process of our invention may be illustrated by, but is not limitedto, the following specific example thereof:

A fused salt bath composed of potassium fluotitanate and sodiumchloride, in which the potassium uotitanate formed 25% of the initialweight of the bath, was electrolyzed -in an electrolytic cell maintainedunder an inert atmosphere of argon gas. For each rmol of potassiumuotitanate that'was decomposed at the cathode, one mol of titanium wasdeposited on the cathode, two mols of potassiumtluoride were formed,four mols of sodium chloride were converted to four mols of sodiumfluoride, and two mols of chlorine gas were evolved from theelectrolyte. Chlorine gas evolved from the fused salt bath at the anodeand titanium metal was deposited on the cathode. Spentelectrolytedepleted in potassium fluotitanate and sodium chloridecontent, and containing a solution of Vhydrochloric acid.

vtion was withdrawn.

sodium fluoride and Vpotassium fluoride in an amount -stoichiometricallyequivalent to the amount of potassium Yfluotitanate electrolyticallydecomposed by the electrolysis, was withdrawn from the electrolytic cellin the vicinityV of the cathode.

The chlorine gas evolved from the electrolytic cell was burned withhydrogen gas to form hydrogen `chloride which, in turn, was absorbed insufficient water to form The spent electrolyte containing potassiumfluoride and sodium fluoride as its essential components was allowed tocool to ambient temperature. The cooled spent electrolyte and theaqueous solution of hydrochloric acid was then introduced into `areaction vessel maintained at about the boiling point of water by meansof steam coils. Also present inthe reaction vessel was a quantity oftitanium dioxide sufficient to react with the potassium fluoride andsodium fluoride content of the spentelectrolyte to form an equivalentamount of potassium fluotitanate, and sufficient water to retain theproducts of tbe reaction in solution.

The spent electrolyte, hydrochloric acid, and titanium dioxide in thehot aqueous medium reacted together to form soluble reaction products.The aqueous solution from the reaction vessel was then introduced intothe third effect of a triple effect evaporator, the temperature of theliquor in which was maintained at about 50 C. Vapor evaporated from 4theliquor in the third effect was withdrawn therefrom by a conventionalcondenser and vacuum pump arrangement. Concentrated liquor from the.third effect was introduced into a separator'from which potassiumfluotitanate crystallized from the solu- The crystallized potassiumfluotitanate was then dried preparatory to introducing this materialinto the fused salt electrolyte contained in the electrolytic cell.

ride was then dried preparatory to introducing this materialinto thefused salt electrolyte.

The concentrated liquor from `the separator of thesecond effect wasintroduced into the first `effect which operated ata temperature ofabout 130 C. Vapor evaporated from the liquor in the first effect wasintroduced into the steam chest ofthe second effect to heat the liquortherein. Concentrated liquor from the first `effect was introduced intothe second effect for further Aconcentration of its salt content.

The potassium tluotitanate obtained from the dryer associated `with theseparator of the third effect and the sodium chloride `obtained .fromthe dryer associated with the separator of the second effect wereintroduced into the fused salt electrolyte being electrolyzed in theelectrolytic cell. The amount of titanium which reacted with thepotassium fluoride and sodium fluoride content of the spent electrolyteand with the vhydrochloric acid was stoichiometrically equivalent to theamount of potassium lluotitanate electrolytically decomposed by the cellto form titanium metal, chlorine gas and spent electrolyte containingpotassium fluoride-and sodium fluoride.

Typical spent electrolytes resulting from the electrolysis of an alkalimetal lluozirconate-alkali metal chloride bath are set forth in acopending application Serial No. 279,471, now Patent 2,687,340.Expressed as ions three such baths are disclosed as follows:

I II III 33.2% N a+ 53% N a* 66% K+ it' if? l? naar 52672 ci- 6% ot- 4%o Each of these spent electrolytes may be readily regenerated inaccordance with our invention by reacting the spent electrolyte with HC1obtained from all of the cell chlorine and with a titanium or, in thisinstance, a zirconium compound such as the carbide, carbonate or oxide,the latter being present in an amount sulicient to provide the amount ofzirconium necessary to form the double fluoride of zirconium and analkali metal when combined with the lluorine content of the spentelectrolyte.

lt will be seen, accordingly, that the process of our invention makespossible the continuous production of titanium or zirconium metal byelectrolysis of a fused salt bath comprising an alkali metal-titanium orzirconium double fluoride and an alkali metal chloride and that ourprocess makes it possible to regenerate these bath component-s from thespent electrolyte without the introduction into the process, either asthe titaniferous or zirconiferous source material or as the digestingmedium for these materials, of any elements which would tend toaccumulate in the cyclic operation which characterizes our process. Theonly extraneous elements introduced into our process are limited tochlorine, oxygen, carbon and hydrogen, and each of these elementsultimately is consumed in the formation of water or a permanent gaswhich is readily discharged from the process as outlined hereinbefore.The relatively expensive components of the system, particularly theiluorine and alkali metal components, are thus continuously recycled.The commercial appeal of the electrolytic production of titanium andzirconium metal is thereby enhanced and an integrated process isobtained in which only relatively simple forms of raw materials arerequired for the continuous production of these metals in a state ofhigh purity.

We claim:

l. In the production of ametal of the group consisting of titanium andzirconium wherein a fused salt bath consisting essentially of an alkalimetal chloride and a double fluoride of an alkali metal and a metal ofthe group consisting of titanium and zirconium in electrolyticallydecomposed with (l) the resulting production of an electrodeposit ofsaid metal on a cathode, (2) the evolution of chlorine gas at an anodeand (3) the formation ot' a spent electrolyte consisting essentially ofat least one alkali metal fluoride; the improvement which comprisesregenerating `material suitable for reuse as the fused salt bath in theaforesaid electrolytic process from said evolved chlorine and said spentelectrolyte as follows: reacting the evolved chlorine with hydrogen toform hydrogen chloride; heating to upto about C. an aqueous solution ofthe spent electrolyte and said hydrogen chloride and a compound of saidmetal from the group consisting of compounds of the said metal and atleast one element of the group consisting of oxygen and carbon in whichthe relative amounts of alkali metal, halogen and metal values presentare substantially the stoichiometric amounts necessary to produce thedesired double fluoride of an alkali metal and the metal of the groupconsisting of titanium and zirconium and recovering said double fluorideand said alkali chloride produced in said heated solution for reuse in arepetition ofthe electrolysis.

2. In the production of a metal of the group consisting of titanium andzirconium wherein a fused salt bath consisting essentially of an alkalimetal chloride and a double fluoride of an alkali metal and a metal ofthe group consisting of titanium and zirconium is electrolyticallydecomposed with (l) the resulting production of an electrodeposit ofsaid metal on a cathode, (2)) the evolution of chlorine gas at an anodeand (3) the formation of a spent electrolyte consisting essentially ofat least one alkali metal fluoride; the improvement which comprisesregenerating material suitable for reuse as the fused salt bath in theaforesaid electrolytic process from said evolved chlorine and said spentelectrolyte as follows: reacting the evolved chlorine with hydrogen toform hydrogen chloride; heating to up to about 100 C., an aqueoussolution of the spent electrolyte and said hydrogen chloride and anoxide of said metal in which the relative amounts of alkali metal,halogen and metal values present are substantially in thestoiclliometric proportions necessary for the formation of a doublefluoride of said metal and an alkali metal and an alkali metal chlorideand recovering said double fluoride and said alkali chloride from saidheated aqueous solution for reuse in a repetition of the electrolysis.

3. In the production of a metal of the group consisting of titanium andzirconium wherein a fused salt bath consisting essentially of sodiumchloride and a double fluoride of potassium and a metal of the groupconsisting of titanium and zirconium is electrolytically decomposed with(l) the resulting production of the electrodeposit of said metal on acathode, (2) the evolution of chlorine gas at an anode and (3) theformation of a spent electrolyte consisting essentially of alkali metaland halide ions; the improvement which comprises regenerating materialsuitable for reuse as the fused sait bath in the aforesaid electrolyticprocess from said evolved chlorine and said spent electrolyte asfollows: reacting the evolved chlorine with hydrogen to form hydrogenchloride; heating to up to about 100 C., an aqueous solution of thespent electrolyte and said hydrogen chloride and an oxido of said metalVin which the relative amounts of alkali metal, halogen and metal valuespresent are substantially in the stoichiometric proportions necessaryfor the formation of a double fluoride of said metal and an alkali metaland an alkali metal chloride and recovering said double fluoride andsaid alkali chloride for reuse in a repetition of the electrolysis.

4. In the production of a metal of the group consisting of titanium andzirconium wherein a fused salt bath consisting essentially of an alkalimetal chloride and a double fluoride of an alkali metal and a metal ofthe group consisting of titanium and zirconium is electrolyticallydecomposed with l) the resulting production of an electrodeposit of saidmetal on a cathode, (2) the evolution of chlorine gas at an anode and(3) the formation of a. spent electrolyte consisting essentially of atleast one ava-1,405

7 alkali metal fluoride; the improvement which comprises regeneratingmaterial. suitable for reuse as the fused salt ybath in the aforesaidelectrolytic process from said evolved chlorine with hydrogen to formhydrogen chloride; heating to up to about 100 C., an aqueous solution ofthe spent electrolyte and said hydrogen chloride and a compound of saidmetal from the group consisting of compounds of said metal and at leastone of the following carbon and oxygen, in which the relative amounts ofalkali metal, halogen and metal of the group consisting of titanium andzirconium present are Substantially the stoichiometric proportionsnecessary for the formation of anaqueous medium containing a doublefluoride of said metal and an alkali metal and an alkali metal chloride;charging the aqueous medium to the third effect of a triple effectevaporator and therein concentrating the aqueous medium to an extentsufficient to promote crystallization therefrom of the double fluoride;crystallizing the double fluoride, recovering the crystallized doubleiluoride Vfrom the effluent from the third effect of the evaporator;delivering the remaining aqueous medium to the References Cited in thetile of this patent UNITED STATES PATENTS 1,801,661 Collngs Apr. 2l,1931 2,144,339 Laist lan. 17, 1939 Y 2,687,340 Wainer Aug. 24, i954FOREIGN PATENTS 574,832 Great Britain g Ian. 22, 1946 OTHER REFERENCESJournal of Applied Chemistry (U. S. S. RJ, vol. i3, 1940, pages 51 thru55; paper by Sklarenko et al.

1. IN THE PRODUCTION OF A METAL OF THE GROUP CONSISTING OF TITANIUM ANDZIRCONIUM WHEREIN A FUSED SALT BATH CONSISTING ESSENTIALLY OF AN ALKALIMETAL CHLORIDE AND A DOUBLE FLUORIDE OF AN ALKALI METAL AND A METAL OFTHE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM IN ELECTROLYTICALLYDECOMPOSED WITH (1) THE RESULTING PRODUCTION OF AN ELECTRODEPOSIT OFSAID METAL ON A CATHODE, (2) THE EVOLUTION OF CHLORINE GAS AT AN ANODEAND (3) THE FORMATION OF A SPENT ELECTROLYTE CONSISTING ESSENTIALLY OFAT LEAST ONE ALKALI METAL FLUORIDE; THE IMPROVEMENT WHICH COMPRISESREGENERATING MATERIAL SUITABLE FOR REUSE AS THE FUSED SALT BATH IN THEAFORESAID ELECTROLYTIC PROCESS FROM SAID EVOLVED CHLORINE AND SAID SPENTELECTROLYTE AS FOLLOWS: REACTING THE EVOLVED CHLORINE WITH HYDROGEN TOFORM HYDROGEN CHLORIDE; HEATING TO UP TO ABOUT 100* C. AN AQUEOUSSOLUTION OF THE SPENT ELECTROLYTE AND SAID HYDROGEN CHLORIDE AND ACOMPOUND OF SAID METAL FROM THE GROUP CONSISTING OF COMPOUNDS OF THESAID METAL AND AT LEAST ONE ELEMENT OF THE GROUP CONSISTING OF OXYGENAND CARBON IN WHICH THE RELATIVE AMOUNTS OF ALKALI METAL, HALOGEN ANDMETAL VALUES PRESENT ARE SUBSTANTIALLY THE STOICHIOMETRIC AMOUNTSNECESSARY TO PRODUCE THE DESIRED DOUBLE FLUORIDE OF AN ALKALI METAL ANDTHE METAL OF THE GROUP CONSISTING OF TITANIUM AND ZIRCONIUM ANDRECOVERING SAID DOUBLE FLUORIDE AND SAID ALKALI CHLORIDE PRODUCED INSAID HEATED SOLUTION FOR REUSE IN A REPETITION OF THE ELECTROLYSIS.